Project Summary This is an exploratory/developmental proposal (R21) to explore brain mechanisms of implicit timing (i.e. timing without awareness) using a novel transgenic mouse that enables high-throughput optogenetics and behavior. The topic is important, because implicit timing forms the basis of temporal expectancy which is at the core of nearly all cognitive function. A recent human fMRI study demonstrated that implicit timing occurred in the inferior olive, a brainstem structure that projects to the cerebellum. The experiment demonstrated, quite unexpectedly, that the inferior olive was activated by 100-200 ms deviations in the timing of stimuli that were not consciously detected. We, and others, have proposed that the unique physiological properties of the inferior olive notably, the propensity of its neurons to generate clock-like subthreshold oscillations (STOs) in membrane potential - are a physiological basis for its role in implicit timing. Although grounded in membrane physiology, the hypothesis of the inferior olive as a clock has remained more hypothetical than proven. The goal of this R21 proposal would be to explore the ability to specifically manipulate STOs within the in vivo inferior olive optically as mice learn about sensory events using implicit timing. The experiments would be a first rigorous test of the timing hypothesis of olivocerebellar clock operations, a hypothesis that has been spiritedly debated for over 25 years but now can be tested directly using optogenetics. A paradigm of implicit timing for which the IO has been implicated is classical conditioning of the eyeblink reflex, which we will use for our in vivo experiments. More generally, our proposal will establish multiple methods to enable high-throughput optogenetics, electrophysiology, and behavior that will have wide utility.